1. Field of the Invention
This invention relates to a process for producing decorative three-dimensionally structured coatings from polyurethane foam on a substrate.
2. Description of Prior Art
Polyurethane foams are based on three components:
A: polyisocyanates; PA1 B: polyols; and PA1 C: auxiliaries, optionally including blowing agents.
The polyurethane is obtained by polyaddition of dihydric and/or polyhydric alcohols (B) and isocyanates and/or prepolymers with terminal isocyanate groups (A). Auxiliaries (C) are known catalysts, stabilizers, pigments, blowing agents, surfactants, emulsifiers, foam stabilizers, flame retardants, fillers, antioxidants, antistatic agents and biocides.
Polyurethane foam is produced either by a chemical blowing process, based on the reaction between isocyanate and water which yields CO.sub.2 as blowing gas, or by the physical blowing process with low boiling point blowing agent components, such as halogenated hydrocarbons and/or readily volatile nonhalogenated hydrocarbons, such as pentane, cyclopentane, propane, isobutane, and dimethylether.
The raw materials are commercially available as a one-component or two-component mixture for processing into polyurethane foam.
Diphenylmethane-4,4'-diisocyanate (MDI) or 2,4- or 2,6-toluene diisocyanate is preferably used as isocyanate for producing polyurethane foam.
Polyurethane foams which are more flexible are obtained by chemical foaming with polyalkylene glycol ethers as diols and isocyanates as well as water.
Polyurethane foams which are more rigid are obtained with mixtures based on polyols and isocyanates which are foamed using physical blowing agents.
Normally polyurethane foam is processed into finished products by foam molding in closed molds or is used as bonding foam for filling cavities and fastening components in the construction industry, because polyurethane foam is tacky in the nascent state at the beginning of crosslinking and adheres well to many materials, such as wood, metal, concrete, masonry.
German Patent Reference DE-OS 21 12 397 describes a plastics material based on polyurethane foam which can be used as a decorative domestic rendering for internal and external walls in the form of foam wall panels.
Japanese Patent Reference JP 54083524 A discloses foamable paints containing a foamable resin, such as foamable polystyrene, foamable polyethylene or foamable polyurethane and a colorant and a binder, in particular a plastics material such as PVC, polyacrylonitrile or polymethacrylate to which organic or inorganic blowing agents, such as azodicarbonamide or sodium bicarbonate, are added, for painting pictures which, after drying at room temperature, are heated to a temperature of 90 to 200.degree. C. depending on the plastics material, for foaming purposes.
Foamable paints of this type are not suitable for producing domestic renderings used over large areas, as they cannot be heat treated to 200.degree. C. in order to obtain a foam.
European Patent Reference EP-A-0160 716 discloses a process for the production of thin flat insulating layers, whereby a low-boiling solvent comprising a one-component-PUR-mixture is applied to a surface like a lacquer by rolling, spreading, spraying or dipping thereafter, these layers being foamed up to a uniform insulation layer.